The machines used to administer these sprays are often dragged out at the last minute with little in the way of preparation. If it doesn't leak and can produce water at the jets then it is often regarded as being in working order.

You have to consider the monetary value of the chemical cocktail that your sprayer may be carrying. Perform a few checks and a little maintenance, and the tank's valuable cargo will not be wasted in leaks or incorrect administration. Just because the right amount of chemical goes out on each acre doesn't mean it has been administered correctly. Take a little time and check the unit over -- it could save you a few euro.

Here we go through one of the more popular sprayer makes found in Ireland, an 800-litre Hardi LY800. This machine is a 12m boom-sprayer with hydraulic-folding booms and electric controls. Though in its second decade, it is still a very capable machine and there are many similar versions both older and younger -- electric and non-electric controls with manual or hydraulic booms -- still in active service all over the country.

On first inspection, look for damage caused by corrosion to areas of the sprayer with linkages or securing brackets and tank-securing bands. Many of the chemicals that pass through a sprayer are extremely aggressive to metalwork and paint may be the only thing binding two pieces of metal together. So, before you hook up to the tractor, and especially before you load up with water and chemicals, make sure the sprayer's metal frame is sound and can carry the load.

On a machine of this age there is plenty of heavy surface rust bubbling away under the paint. This would really require treatment as metal structures are quite thin to keep weight down, such as on the actual sprayer booms. A wire brush and some red oxide paint should help preserve any rusted or exposed metal.

Before working on the sprayer, though, give it a wash down, preferably with some detergent in the mix to neutralise any nasty residues that may be on the machine's surface. Even performing this task, a wise precaution in protection would be to use a clear face shield and some suitable gloves and overalls to offer some protection against potential chemical residues.

The various products that pass through a sprayer may not just be hard on metal -- the main tank and the machine's overall pipe work and plumbing may also be affected. Have a look around for signs of cracks or perishing in the tank and piping -- particularly where the sprayer booms fold, the pipes may kink here. Replace anything suspect. Check that the PTO shaft tubing and joints are not worn and seized. If the PTO guard is defective, replace rather than risk it.

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Filters

There are two main filters on this machine, a suction screen on the top of the tank and a pressure filter screen in the main filter housing at the front of the machine. Both of these are stainless steel mesh filters and can be removed and cleaned -- again, wear suitable gloves to provide protection from any chemical residues which may be present. There is also a restrictor at the base of the main filter housing which can block as well. There is, of course, another mesh screen at each jet as a final protection against blocking the orifice in each nozzle.

Before removing and inspecting either of the main gauze filters, it would be a good idea to get new o-rings that seal the filter bowl lids/assemblies. These are nearly always swollen with the chemicals or oils that have passed through the sprayer and are impossible to get back into place (a few spare ones would not go amiss as well -- they're not dear).

If you are confident the sprayer is clear of chemicals, having being washed out before storage, fill the tank with some water and open the booms out in a suitable area where you can run the sprayer up to pressure in a 'wet' test. Run it up to your normal maximum pressure to see if there are any leaks that require attention.

Last year we detailed how to prepare a sprayer for winter storage, and the season just passed was certainly cold enough to test any unit.

If there is any frost damage it will be apparent very quickly, with poor or no performance from the sprayer's pump. If the pump has escaped damage, other pipes and valves may not have been so lucky, but again it will be quickly apparent if there is a problem. The triple diaphragm pump used on the Hardi LY800 has been used on several Hardi sprayers. It, plus smaller and bigger variants, are extremely reliable as a rule.

Where there are problems, the Hardi tends to be easy to work on and repair. There is one diaphragm and two valves per chamber, and any loss of function would be indicated by 'pulsing' or an inability to maintain a constant pressure. This could be caused by a stuck valve, split diaphragm or a bearing gone in the crankcase.

A stuck or broken valve will display very few symptoms other than pulsing (also check pressure in pulse diaphragm). A split diaphragm would cause liquid to enter the pump crankcase and exit by ventilation hole. Bearing trouble in the crankcase would usually be heard. Work on the top end of the pump is within many peoples' grasp but the bottom end is not for the faint hearted. If you do tackle the crankcase, make sure you mark everything with dot punching or similar as it comes apart, especially the connecting rods to get the orientation correct -- otherwise you could end up with a pump out of phase.

Pressure

Make sure that the pump drive shaft is greased front and back as this helps to keep contaminants out and lubricated. There is a pulse damper at the top of the pump to help even out the pulses between piston strokes. This is set at two-bar in the factory; this can be adjusted to suit different spraying pressure ranges. Check the condition of the suction damper diaphragm (forward-facing rubber diaphragm) for perishing or leakage.

If you are happy with the plumbing, check the hydraulic rams and pipes for leaks, two double-acting rams fold the booms while a two-stage ram raises and lowers the boom assembly. The two-stage ram works like a trailer-tipping ram and has a set of seals for each stage, so make sure you extend it to the maximum to check its function for leaks. Again, the environment they work in does make them more susceptible to leakage.

Boom function is important. On this machine the booms sagged down by almost 200mm at the ends on both sides and required adjustment on the steel cable to bring them all back level again. There are also adjustable stops on the smaller end sections of the boom.

The entire boom assembly slides on two box sections to adjust the spraying height and enable the booms to be folded and unfolded. Make sure these box sections are freshly greased and the clamped slides are tight enough to prevent vertical boom swaying in the locked position -- but not too tight as to not allow it to lower under its own weight when lowering the hydraulic ram.

There are greasing points on the rams and pivots which do require attention -- even if it is only on an annual basis. Check for wear at these points as well.

Penguins

On the sprayer featured here, there was a substantial amount of wear both at the ram ends and pivots. In rough fields, the booms would resemble penguins flapping and eventually something would have to break.

Finally, and most importantly, there are the jets themselves. These have a lifespan and will wear, producing poor spray patterns and/or increased chemical application beyond their specification. Visually check the spray pattern of each jet by using clean water and under normal working pressures. The spray pattern must be fan-shaped for normal flat spray nozzles.

Hardi states that the precision of the nozzles and their liquid distribution is acceptable with flow rates of up to 10pc above the table values for application. If the flow rate exceeds 10pc of the table value, the nozzles are worn and all nozzles should be replaced.

Hardi has a lot of sprayer information on its website, www.hardi-international.com, from operator's manuals to maintenance guides and an online jet and application calculator. The latter can be used to calculate the appropriate rate in litres/minute for a nozzle at a specific pressure. Using this information, and a calibration jug, all nozzle outputs can be checked for consistency and to see if they are within Hardi's 10pc tolerance range.